For myself, I play on 3 sites although I have played many others.
PokerStars...natch.
Arguably the best interface/platform with the best variety of games/levels. I like the filter option especially.
Customer Service is 2nd to none in my opinion too!
Full Tilt
Coming on strong after PokerStar"s crown. Nice stable interface/platform and a good mix.
Their game/tourney filter is good but not as strong as Stars.
PKR
OK, I heard you all moan but, say what you like (I will in a minute) but, IMHO, it"s the future of online poker.
Sure, they"re only spreading two games (HE & Omaha). Omaha Hi/Lo disappeared more"s the pity.
With their latest software release, it"s less PC resource hungry than before and the new features are a blast.
PKR need to invest in adding more poker variations to attract the more serious players and some improved marketing/sponsorships wouldn"t hurt in getting the word out.
Still a long way to go to challenge the more established market players and Yes, it"s for the PlayStation generation but (or because of that).....it"s full of fish!
If you can"t make money there...you ARE doing something wrong!